Mechanical couplings designed to resolve process constraints

ABSTRACT

An integrated circuit package having a shunt resistor with at least one self-aligning member that protrudes from a first surface, and a lead frame with at least one self-aligning feature that is a cavity within which the at least one self-aligning member is located, and an integrated circuit located on the lead frame.

This application is a continuation of U.S. application Ser. No.15/857,988, filed Dec. 29, 2017, the contents of which is hereinincorporated by reference in its entirety.

BACKGROUND

Semiconductor devices can be used as amplifiers dedicated to current orvoltage sensing. The amplifier typically comprises an integrated circuit(IC) package that is typically coupled to a lead frame that is furtherattached to a shunt resistor to increase area of the circuit boardoccupied by these elements. Attaching the lead frame to the shuntresistor, however, has proven difficult, as the alignment of the twocomponents can be disrupted during the prior art methods or processes ofepoxy or solder attachment. Accordingly, a device and process are neededto ize the misalignment of the lead frame and the shunt.

SUMMARY

One aspect of the present disclosure provides an integrated circuitpackage. The package comprises a lead frame, an integrated circuitlocated on the lead frame and a self-aligning shunt resistor coupled tothe lead frame and to the integrated circuit. The shunt resistor coupledto the lead frame through the use of self-aligning members. In oneaspect of the disclosure, the shunt has at least two self-aligningmembers that protrude from a first surface facing the lead frame thatextend past a second surface of the lead frame opposite a first surfaceof the lead frame facing the shunt. In a further aspect of thedisclosure, the self-aligning members extend through a self-aligningfeature in the lead frame. In still a further aspect of the disclosure,the self-aligning members have at least a portion that extends past theself-aligning feature and has a larger surface area than theself-aligning feature of the lead frame.

In an alternative aspect of the disclosure, the self-aligning members ofthe shunt extend past a surface of the lead frame facing the shunt. In afurther aspect of the disclosure, the self-aligning features cavitiesforming at least two sidewalls. In a further aspect of the disclosure,the self-aligning members are affixed to the sidewalls of theself-aligning features. In a further aspect of the disclosure, theself-aligning members are affixed to the sidewalls of the self-aligningfeatures by epoxy coupling. In an alternative aspect of the disclosure,the self-aligning members are affixed to the sidewalls of theself-aligning features by solder coupling. In alternative aspects of thedisclosure, other methods of affixing the self-aligning members areaffixed to the sidewalls of the self-aligning features can be used.

In a further aspect of the disclosure of the package, the shunt has itsown integrated external leads. In a further aspect of the disclosure,the package is an amplifier for current or voltage measurements. Theamplifier comprises the above-described packages, wherein the shunt hasits own external leads, or, has a low-resistance coupling to externalleads of the lead frame. A mold encompasses the lead frame, the shuntresistor, and the integrated circuit, except for the integrated externalleads of the lead frame or the integrated external leads of the shuntresistor.

Another aspect of the present disclosure is method of manufacturing theabove-described integrated circuit packages. The method comprisesforming a lead frame, forming self-aligning features in the lead frame,forming a shunt, forming at least two self-members on the shunt. Themethod further comprises coupling the shunt to the lead frame byinserting the self-aligning members of the shunt into the self-aligningfeatures of the lead frame. The method further comprises forming anoutermost surface of at least one self-aligning member having a surfacearea that is greater than a surface area of the self-aligning feature ofthe lead frame.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 illustrates an aspect of the disclosure of an integrated circuitpackage having a shunt and a lead frame are coupled together;

FIGS. 2A-2F illustrate an aspect of the disclosure of fabricating theFIG. 1 integrated circuit package;

FIGS. 3A-3B illustrates a second aspect of the disclosure of a shunt anda lead frame are coupled together;

FIG. 4 illustrates a precursor of the FIG. 3A/3B device; and

FIGS. 5A-5B illustrate block diagrams of another aspect of the presentdisclosure of an amplifier having an integrated circuit package having ashunt and a lead frame are coupled together.

DETAILED DESCRIPTION

Certain terms have been used throughout this description and claims torefer to particular system components. As one skilled in the art willappreciate, different parties may refer to a component by differentnames. This document does not intend to distinguish between componentsthat differ in name but not function. In this disclosure and claims, theterms “including” and “comprising” are used in an open-ended fashion,and thus should be interpreted to mean “including, but not limited to .. . .” Also, the term “couple” or “couples” is intended to mean eitheran indirect or direct wired or wireless connection. Thus, if a firstdevice couples to a second device, that connection may be through adirect connection or through an indirect connection via other devicesand connections.

As part of the present disclosure, it was recognized that prior methodsof epoxy and/or solder coupling of a shunt to a lead frame resulted innon-alignment or rotation during the liquid phase of the solder reflowprocess. Similarly, a shunt can rotate as a result of epoxy coupling toa lead frame.

To prevent such an occurrence, it was found that forming self-aligningmembers and self-aligning features in the shunt and lead frame,respectively, can alleviate and minimize the rotation that typicallyoccurs with prior methods of coupling the two components.

FIG. 1 illustrates an integrated circuit package 100 in accordance withthis disclosure. The integrated circuit package 100 has a shunt 110 anda lead frame 120. The shunt has at least one self-aligning member 115that protrudes from a first surface of the shunt 111 facing the leadframe and extend past a second surface 122 of the lead frame opposite afirst surface 121 of the lead frame facing the shunt 121. In the exampleshown, the two self-aligning members 115 have at least a portion 116that extends past the self-aligning feature 125 and has a first width117 that is greater than a second width 127 of the self-aligning feature125 of the lead frame 120.

FIGS. 2A-2F show an aspect of the disclosure of fabricating theintegrated package 100 of FIG. 1. As illustrated in FIG. 2A, a shuntprecursor 110′ and a lead frame precursor 120′ are both depicted. FIG.2B shows the formation of self-aligning members 115 protruding from theshunt 110 and the formation of self-aligning features 125 within thelead frame 120. While the self-aligning members 115 is described asbeing formed from the shunt precursor 110′ material, it should beunderstood that the self-aligning members 115 are not so limited. Forexample, self-aligning members could be formed of a different material,and can be affixed to a surface of the shunt 111 (FIG. 1) facing thelead frame 120. Alternatively, the self-assembled members could beformed through molding of the shunt in a manner having the self-alignedmembers. The illustrated self-aligning members 115 of FIG. 2B are madefrom a punch down tool 170 and a complementary punch up tool 180.

Similarly, the FIG. 2B self-aligning features 125 of the lead frame 120are illustrated as being formed by a punch down tool 190 and clamp 195.It should be noted that such an example is not limiting. For example,other methods of forming the self-aligning features 125 can be used likeconventional etching. Alternatively, the lead frame can be molded toinclude the self-aligning features upon formation. In the exampleillustrated, the self-aligning features 125 are shown as through holes,but it should be understood that the illustration is not so limiting.For example, in an alternative example, the self-aligning feature can bea cavity having at least two sidewalls and no through hole. Like theexample illustrated in FIG. 2B, these alternative examples can be formedwith a punch down tool 190 and a clamp 195, with the difference beingthe height of the punch down tool (the height being measured from afirst surface 121 of the lead frame facing the shunt 110 to the secondsurface 122 of the lead frame opposite the first surface 121). In thealternative example, the cross-sectional height of the punch down toolwould be less than the cross-sectional height of the lead frame withinwhich the cavities would be formed.

FIG. 2C illustrates the shunt 110 and the lead frame 120 without thepunch down and punch up tools 170, 180, 190, and clamp 195.

As illustrated in FIG. 2D, the self-aligning members 115 are insertedthrough the self-aligning features 125 such that they extend past asecond surface 122 of the lead frame 120 opposite a first surface 121 ofthe lead frame facing the shunt. As discussed above, the example is notlimiting. For example, the example illustrated in FIG. 2D showsself-aligning features 125 as through holes. As discussed above, theself-aligning features could also be formed as cavities having at leasttwo sidewalls and not having a through hole. The self-aligning memberswould be complimentary in height to the cavities (with the height beingmeasured from a first surface 121 of the lead frame facing the shunt 110to the second surface 122 of the lead frame opposite the first surface121). In a further alternative example, the self-aligning members can beaffixed to the self-aligning features of the lead frame either by epoxyor solder or some other fastening mechanism.

The insertion of self-aligning members 115 into the self-aligningfeatures 125 minimizes and possibly eliminate any rotation of the shunt110 relative to the lead frame 120 as with the prior art. Because thereare at least two self-aligning members 115 inserted into theself-aligning features 125, any rotation during further processing stepscan be minimized and/or eliminated.

In a further example of the fabrication process illustrated in FIG. 2E,portion 116′ of the self-aligning members 115 extend past a secondsurface 122 of the lead frame 120 that is opposite the first surface 121of the lead frame 120 that faces the shunt 110. A punch up tool 197 ispositioned underneath the lead frame 120 having feet 198 aligned withthe self-aligning members 115 extending through the self-aligningfeatures. A clamp 199 is positioned over the shunt 110 to act as abackstop for the impact that the punch up tool 197 would create uponimpact on the portions 116′ of the self-aligning members 115. The impactof the punch up tool 197 creates portions 116 of the self-aligningmembers 115 having a larger surface area 117 (FIG. 2F) than the surfacearea 127 (FIG. 2F) of the opening that forms the self-aligning feature125 of the lead frame 120. The self-aligning members 115 act ascouplings to couple the shunt 110 to the lead frame 120.

The resulting device is illustrated in FIG. 2F.

By having self-aligning members 115 that mate with self-aligningfeatures 125, the risks of rotation during assembly are minimized by upto 50% relative to prior methods using epoxy or solder coupling. Theself-aligning members 115 and self-aligning features 125 allow forinterlocking that can also shorten production time by eliminating thetime-consuming process of epoxy or solder coupling step, which requiresheating, attachment, and cooling of the epoxy or solder used to hold thematerials together. In addition, it eliminates the expense of epoxy andsolder that are required for prior methods of coupling the shunt to thelead frame.

In another example depicted in an angled plan view in FIG. 3A, anintegrated circuit package 200 has a lead frame 220 placed over a shunt210. In this example, the shunt has at least four self-aligning members215 that are shown to extend through the self-aligning features 225 ofthe second surface 222 of the lead frame 220 opposite the first surface221 of the lead frame. As illustrated, two portions 216′ of twoself-aligning members 215 are depicted prior to the punch up tool (197of FIG. 2E) and clamp (199 of FIG. 2E) have deformed those portions. Theother two portions 216 of two self-aligning members 215 are depictedafter the punch up tool (197 of FIG. 2E) and clamp (199 of FIG. 2E) havedeformed those portions. As illustrated, those portions 216 have largersurface areas 217 than the surface areas 227 of the self-aligningfeature 225 of the lead frame 220. In the example illustrated, thesurface areas 217 and 227 are equivalent to the circular diameters (asmeasured from a top plan view of FIGS. 3A and 3B) of portions 216 of theself-aligning members 215 and the self-aligning features 225,respectively. It should be noted that this is not intended to belimiting. For example, the surface areas 217 and 227 could have a topplan view shape of a rectangle, triangle, or some other shape.

FIG. 3B illustrates a further aspect of the disclosure in which aconductive paste 250 is placed on the shunt 210 or lead frame 220. Aftercoupling, conductive paste 250 can fill any mechanical gaps between theshunt 210 and lead frame 220. This can enhance the electrical andthermal conductivity of the device.

FIG. 4 illustrates a blown-apart depiction of a shunt 310 over a leadframe 320 with a punch up tool 397. In this example, the shunt 310 hasfour self-aligning members 315 (only two of which are illustrated). Theself-aligning members 315 are shown prior to their deformation by thepunch up tool 397. It should be noted that once the punch up tool 397 isremoved, an integrated circuit can be coupled to the lead frame.Alternatively, an integrated circuit can be seated on the lead frameprior to the punch up tool 397 step.

FIGS. 5A and 5B illustrate block diagrams of another aspect of thepresent disclosure. An amplifier 600 for current or voltage measurementscomprises an IC package 610. The package 610 can be any of theabove-described examples of the IC packages. The package 610 includes alead frame 620, IC 622 on the lead frame 620, and shunt resistor 624.The shunt resistance 624 is coupled to the lead frame 620 (as discussedabove) and electrically connected to the IC 622. The lead frame 620 andshunt resistor 624 are coupled together through self-aligning membersand self-aligning features as described above with respect to FIGS. 1-4.The shunt resistor 624 can have its own external leads, or, has alow-resistance coupling to external leads of the lead frame.Additionally, the package 610 includes a mold 626 that encompasses thelead frame 620, shunt resistor 624, and IC 622, except for the externalleads of lead frame 620 or shunt resistor 624.

One of ordinary skill in the art would be familiar with various possibleconfigurations the amplifier 600 could have to facilitate a current- orvoltage-sensing function. For example, the shunt resistor 624 can becoupled via its own external leads, or, via external leads of the leadframe 620, to an input device 630 and to a load device 635. FIG. 5Apresents a low-side sensing configuration. FIG. 5B presents a high-sidesensing configuration. One skilled in the art would appreciate the othersensing configurations that could be used. In some examples, to measurethe current (I_(device)) passing through the input device 630, thevoltage potential drop (V_(in)) across the shunt resistor 624, is readas an input to the IC 622, to produce an output voltage (V_(out)) fromwhich I_(device) can be calculated.

The amplifier 600 can further comprise additional components tofacilitate the measurement of current or voltage. For example, theamplifier 600 can also include a calibration circuit 640 that iselectrically connected to the IC 622. The calibration circuit 640 canalso be encompassed by the mold 626, or, can be external to the mold626. The calibration circuit 640 can be configured to facilitateadjustment of the gain of the amplifier IC 622, using procedures wellknown to those skilled in the art. E.g., the calibration circuit 640 caninclude a network of parallel resistors, each resistor having adifferent value in a desired range governed by design considerations. Insome examples, the parallel resistors of the calibration circuit 640comprise the same low TCR material used to form the shunt resistor 624,or, in other cases is included in other topological configurations. Thecalibration circuit 640 can be connected via conventional input/outputlead 645 to the IC 622, and via a data bus 650, to a conventionalcalibration system 660 that is external to the package 610.

The above discussion is meant to be illustrative of the principles andvarious examples of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. For example, it should be notedthat the lead frame could include an epoxy or solder coupling inaddition to the self-aligning members and self-aligning features thatcouple the shunt to the lead frame. It should also be noted that theshunt and/or lead frame can be made of a material having a hightemperature co-efficient of resistivity (TCR). It should also be notedthat while certain examples above have been illustrated as a quad flatno-lead package (QFN), other conventional type of lead-containingpackage, including plastic dual in-line integrated circuit packages(PDIP), small outline integrated circuits (SOICs), quad flat packages(QFP), thin QFPs (TQFPs), low profile QFPs (LPQFPs), Small ShrinkOutline Plastic packages (SSOP), thin SSOPs (TSSOPs), thin verysmall-outline packages (TVSOPs), or other packages well known to thoseskilled in the art. It should also be noted that other layers not showncan be included in the packages described above. In addition, it shouldbe understood that other components including bonding wires, mountingpads, tie bars, and other components can be included in the examplesdescribed above.

It is intended that the following claims be interpreted to embrace allsuch variations and modifications.

What is claimed is:
 1. An integrated circuit package, comprising: a padincluding a cavity; at least one lead extending from the pad; a resistorincluding a member that extends from a first surface of the resistor,the member within the cavity such that the resistor is electricallyconnected to the pad; an integrated circuit die electrically connectedto the resistor.
 2. The integrated circuit package of claim 1, whereinresistor is a shunt resistor.
 3. The integrated circuit package of claim1 further comprising a conductive paste between the member and thecavity.
 4. The integrated circuit package of claim 1, wherein the cavityextends from a first side of the pad to a second side of the pad.
 5. Theintegrated circuit package of claim 5, wherein the member protrudesbeyond a plane along a surface of the second side of the pad.
 6. Theintegrated circuit package of claim 1, wherein the pad is located belowa plane along a surface of the at least one lead.
 7. An integratedcircuit package, comprising: a shunt resistor having at least one memberthat protrudes from a first surface of the shunt resistor; and a portionof a lead frame having at least one a cavity extending from a firstsurface of the portion of the lead frame facing the first surface of theshunt resistor, the at least one member located within the at least onecavity; and an integrated circuit located on the portion of the leadframe.
 8. The integrated circuit package of claim 7, wherein the cavityis a through hole that extends from the first side of the portion of thelead frame through a second side of the portion of the lead frame, thatis opposite the first side of the portion of the lead frame.
 9. Theintegrated circuit package of claim 8, wherein an outermost surface ofthe at least one self-aligning member has a surface area that is greaterthan a surface area of the self-aligning feature of the portion of thelead frame.
 10. The integrated circuit package of claim 7, wherein theintegrated circuit package is a quad flat no-lead (QFN) package.
 11. Theintegrated circuit package of claim 7, wherein the shunt resistor has atleast four members.
 12. The integrated circuit package of claim 7,wherein the at least one member protrudes beyond a plane of the portionof the lead frame.
 13. The integrated circuit package of claim 7,wherein the at least one member includes a feature resultant of stampingat one end.
 14. An amplifier comprising: an integrated circuit packagecomprising: a shunt resistor having at least two self-aligning members,each of the at least two self-aligning members being formed from amaterial of the shunt resistor and as protrusions from a first surfaceof the shunt resistor; and a pad of a portion of a lead frame having atleast two holes extending from a first surface of the pad facing thefirst surface of the shunt resistor through a second surface of the padopposite the first surface, wherein each of the at least twoself-aligning members are located within and through a respective one ofthe at least two holes; and an integrated circuit located on said leadframe.
 15. The integrated circuit package of claim 14, wherein the atleast two self-aligning members protrude beyond a plane of the portionof the pad.
 16. The integrated circuit package of claim 14, wherein theat least two self-aligning members include a feature resultant ofstamping at one end.